When a guest shows up with a sponge cake in Japan you can get excited. In fact the sponge cake is thought to be one of the first of the non-yeasted cakes dating back to the 17th century.
This cake’s color is very deep due to the type of egg used. This is known as Nagoya’s Cochin chicken egg sponge cake, a sponge cake that uses chickens unique to Aichi prefecture called Pyorin.
In this case the whole-egg has been used unlike some other sponge cakes for which yolks and egg whites are beaten separately. The eggs, and sometimes extra yolks, are beaten with sugar and heated at the same in a bain-marie to a stage known to patissiers as “ribbon stage”.